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Climate Hustle

Has sea level rise accelerated since 1880?

Posted on 7 April 2011 by Tamino

Many thanks to Tamino from Open Mind for allowing SkS to republish his post So What? as the rebuttal to "sea level rise is decelerating".

A paper by Houston & Dean studies 57 tide gauge records from the U.S. (including Hawaii and oceanic territories) and concludes that sea level rise has not accelerated. In fact the authors seem to go out of their way to state that the average result shows deceleration at every opportunity. But there are some big questions about their analysis. Why do they use tide gauge records from just U.S. stations? Why not a global sample? Why use individual tide gauge records when we have perfectly good combinations, from much larger samples, which give a global picture of sea level change and show vastly less noise? Why do they restrict their analysis to either the time span of the individual tide gauge records, or to the period from 1930 to 2009? Why do they repeatedly drone on about “deceleration” when the average of the acceleration rates they measure, even for their extremely limited and restricted sample, isn’t statistically significant?

But the biggest question of all is: what’s the big deal?

Here’s some sea level data, in fact two data sets. One is a global combination of tide gauge records by Domingues et al. (2008, Nature, 453, 1090-1094, doi:10.1038/nature07080). Using around 500 tide gauge records globally, it’s the latest version of the “Church & White” dataset. The other is satellite data:

I averaged the two data sources during their period of overlap, and computed a smoothed version:

This is a global data set, and it’s a worldwide average so its shows vastly less noise than individual tide gauge records. We could even use it to look for acceleration or deceleration in sea level rise. But one thing we should not do is restrict consideration to the quadratic term of a quadratic polynomial fit from 1930 onward. That would be pretty ignorant — maybe even misleading.

As so often happens, one thing to be cautious of is that the noise shows autocorrelation. As Houston & Dean point out, the Church & White data since 1930 are approximately linear, so to get a conservative estimate of the autocorrelation I used the residuals from a linear fit to just the post-1930 data and fit an ARMA(1,1) model.

If we compute the linear trend rate for all possible starting years from 1880 to 1990, up to the present, we get this:

According to this, the recent rate of sea level rise is greater than its average value since 1930. Significantly so (in the statistical sense), even using a conservative estimate of autocorrelation. But the increase itself hasn’t been steady, so the sea level curve hasn’t followed a parabola, most of the increase has been since about 1980. How could Houston & Dean have missed this?

Here’s how: first, they determined the presence or absence of acceleration or deceleration based only on the quadratic term of a quadratic fit. That utterly misses the point. Changes in the rate of sea level rise don’t have to follow a parabola, since 1930 or any time point you care to name. In fact, by all observations and predictions, they have not done so and will not do so.

Second, by using individual tide gauge records, the noise level is so high that you can’t really hope to find acceleration or deceleration of any kind, with any consistency. Not using quadratic fits, and certainly the non-parabolic trend which is present can’t be found in such noisy data sets.

Even so, we can also fit a quadratic (as Houston & Dean did), and estimate the acceleration (which is twice the quadratic coefficient):

Well well … it looks like starting at 1930 is the way to get the minimum “acceleration” by this analysis method. Could that be why Houston & Dean chose 1930 as their starting point?

If we restrict to only the data since 1930, as Houston & Dean did, and fit a quadratic trend, we get this:

Can you tell, just by looking, whether it curves upward or downward? Clearly, the parabolic fit doesn’t show much acceleration or deceleration, if any. We can get a better picture by first subtracting a linear fit, then fitting a parabola to the residuals?

That answers the question: the quadratic fit shows acceleration in the Church & White data. But, when autocorrelation is taken into account, the “acceleration” is not statistically signficant.

But — just because the data don’t follow a parabola, doesn’t mean that sea level hasn’t accelerated. Let’s take those residuals from a linear model, and fit a cubic polynomial instead:

Well well … there seems to be change after all, with both acceleration and deceleration but most recently, acceleration. And by the way, this fit is significant.

And now to the really important part, which is not the math but the physics. Whether sea level showed 20th-century acceleration or not, it’s the century coming up which is of concern. And during this century, we expect acceleration of sea level rise because of physics. Not only will there likely be nonlinear response to thermal expansion of the oceans, when the ice sheets become major contributors to sea level rise, they will dominate the equation. Their impact could be tremendous, it could be sudden, and it could be horrible.

The relatively modest acceleration in sea level so far is not a cause for great concern, but neither is it cause for comfort. The fact is that statistics simply doesn’t enable us to foresee the future beyond a very brief window of time. Even given the observed acceleration, the forecasts we should attend to are not from statistics but from physics.

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Comments 1 to 50 out of 109:

  1. Thanks Tamino. Worth adding that this latest Church and White data set (with tide gauge data updated to 2010) shows a trend that is close to the altimeter record trend over the entire altimeter period. This should reduce any doubts raised in the paper about the altimetry record. Both records are significantly higher than the 20th century average of around 1.8mm/yr, indicating a recent increase in trend.

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  2. The GIA corrected altimeter trend is 3.2 +/- 0.4 mm/yr and the GIA corrected tide gauge data trend is 2.8 +/- 0.8mm/yr over the same altimetry period since 1993. The new Church and White 2011 paper is available. It also has a clearer chart than mine! (figure 4)

    Another assumption made in the Houston and Dean paper is that GIA uplift rates for the Northern US coast are stable, whereas there is some evidence of accelerating uplift in the North Atlantic as a result of increasing Ice loss, see for example Jiang 2010 . Any small regional acceleration in uplift would reduce effective tide gauge recorded rate of msl increase.
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  3. Sea level has been rising for the past 20,000 years. In some parts of the world (eg Scandinavia)it's been dropping. Here in Sydney it's increased about 8mm over 25 years, though nothing much in the last decade.

    Looking at the curve fit in the last graph, which is claimed as significant, I couldn't help laughing. What is the level of significance? It looks to me like it could just as easily have a downward line drawn through it with no significance.

    Looking at the charts around the world, I find it hard to really see acceleration in recent times.
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  4. I take a rather simplistic view - I'll be interested when the water starts lapping over some islands. These effects are really very minimal. A few mms over decades? I mean - put a bit more cement on top of your sea wall...abandon that pontoon and build a new one...move your settlement a few feet up the hillside. These are not cataclysmic effects - no more cataclysmic than say a port getting silted up.

    We will have cracked carbon reduction long before these sorts of figures give us serious cause for concern.
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  5. 'It looks to me like it could just as easily have a downward line drawn through it with no significance.'

    Then why dont you run the regression test and show us? What mathematical method do you propose will give you a downward line?

    As to past sealevel rise. The questions are:
    1/ Why did is rise in the past and do those reasons apply now?
    2/ What was the RATE of sealevel rise globally over last 5000 years? (hint very, very small).

    Also individual tide guages are subject to local tectonics. Do really believe your anecdotes about sydney and Scandinavia constitute a scientific statement about global sealevel rise? Especially compared to the proper methodology of Church and White?
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  6. daniel maris#4: "I'll be interested when the water starts lapping over some islands. These effects are really very minimal."

    Fast forward 30-50 years; suppose mean sea level is up approx 0.75 meters from today. Go to a place that is actively subsiding such as anywhere on the coast of South Louisiana. Add in a hurricane with even a modest storm surge. Not quite so minimal anymore.

    Now put that event at Port Fourchon, La (mean elevation 0); its the terminal for the Lousiana Offshore Oil Port (which handles 15% of US annual imports). It also services 90% of the deepwater rigs and half of the shallow water rigs in the Gulf of Mexico.

    From a 2008 impact study:
    We conservatively estimate that a three-week loss in services from Port Fourchon would lead to:
    • A loss of $9,994.7 million in sales at U.S. firms;
    • A loss of $2,890.9 million in household earnings in the U.S., and;
    • A loss of 77,440 jobs in the nation.
    The longer it takes to restore activity at the port or the longer it takes to shift services to other ports along the coast, the greater these losses will be.

    Definitely not so minimal any more. And even if we have 'cracked' carbon reduction by then, that won't halt sea level rise for a long while.

    Any relation to Roger Maris of NY Yankees fame?
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  7. Daniel, you are joking? How about issues we face now? Salt contamination of farmland on deltas; roadways, farms and houses under threat from coastal erosion - hell, my city is dithering on whether to fight or retreat for large hunk of it in the long term. Salt is already a problem and the dune barrier takes a hammering in high seas. Problems start LONG before things go underwater. If we get 10mm/yr, that's catastrophic. Lets just not.
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  8. daniel maris @4, while I agree that the prospective sea level rises over the coming century could be handled very comfortably by advanced economies, I believe you are being far to sanguine.

    During the Eemian epoch, the last interglacial, the mean global surface temperature was 1 to 2 degrees warmer than the those in the middle of the 20th century, ie, 0.3 to 1.3 degrees warmer than today, and around the temperature target currently muted for stabilizing CO2.

    During the Eemian, the sea level was 4 to 6 meters higher than at present - sufficiently high to turn Scandinavia into an island. So that is the sea level, at minimum, we are heading for given sufficient time.

    Of course, glacial melt, the primary source of the sea level rise, is slow. Assuming it rises to the average rate during the last great glacial melt, ie, the end of the last glaciation, then sea levels will eventually be rising at about 15 mm per year, or 1.5 meters per century. It will take a while to ramp up to that, so lets predict about a 1 meter sea rise by 2110. I believe that to be a reasonable estimate.

    Three things should be noted about that:

    1) Even with a 1 meter sea rise, the costs of responding to that, either by building sea walls, or by abandoning properties and shifting to new locations, will be less than the cost of eliminating fossil fuel use from our economies. So if that were the only cost of global warming, perhaps we would be better with BAU. But it is not the only cost - indeed it is probably the smallest prospective cost of global warming, so BAU is not a sensible strategy.

    2) That rate of sea level rise would not stop in 2110, but in fact continue of for another two or three centuries after that. Just factoring in the short term costs is poor planning, particularly when the long term costs will involve either placing a 10 meter plus sea wall around most of the coast line of most nations, or the loss of very significant areas of arable land.

    3) This grim if very slow impact is more or less what we are committed to already. If we go to zero carbon economies by 2050, we are already looking at 4 to 6 meter long term sea level rises. If we continue at BAU, the rise is likely to be much larger.

    Finally, none of this should detract from muoncounter's very excellent response. Although responding to sea level rise is very doable, it involves large scale capital works and/or land resumptions. In other words, it is an expensive project whose benefits will not be fully felt until 20 to 30 years after the event. Governments don't do that sort of project well, so we are likely to experience the cost of sea level rise in increased damage and financial costs from storms. And if we do it that way, the costs will be significantly greater than the costs of eliminating fossil fuel use from our economies.
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  9. How long does it take for sea level rise in the North Atalntic (from Greenland ice sheet melt) to spread worldwide? I recall a Newscientist article which suggested that it may take up to 30 years for a North Atlantic sea level rise to spread out worldwide. Sorry I don't have references but the author suggested that the world's oceans were analogous to a series of bathtubs linked by small hoses rather than a continuous ocean. Given that the Greenland ice sheet is likely to be a much larger contributor to sea level rise than antarctica ice sheets, this is a significant issue.
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    Moderator Response: [DB] The effects of GIS melt on sea levels is indeed discussed by the New Scientist article on the Stammer JGR paper (discussed here). Effects of a collapse of the WAIS are discussed here. Keep in mind that sea level rise is continuous (globally averaging about 3 mm per year currently, but projected to rise significantly with the expected melt). Hansen 2011 discusses scenarios under which 5 meters of SLR can be expected globally by 2100, due to non-linear ice sheet decomposition.
  10. @4. daniel maris:

    "...I take a rather simplistic view - I'll be interested when the water starts lapping over some islands. These effects are really very minimal. A few mms over decades?"

    Daniel, are you forgetting that there is a time delay before large amounts of ice completely melt for any given temperature?

    Also, what about the 1 degree Fahrenheit rise that is in "the pipeline" for the next 30 years? That's assuming that we stop all emissions today. Since that won't happen we have to take at least a bare minimum of 450 ppm into account (still unrealistic).
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  11. daniel maris wrote : "I take a rather simplistic view - I'll be interested when the water starts lapping over some islands. These effects are really very minimal. A few mms over decades? I mean - put a bit more cement on top of your sea wall...abandon that pontoon and build a new one...move your settlement a few feet up the hillside. These are not cataclysmic effects - no more cataclysmic than say a port getting silted up."

    There's plenty of information out there that shows that maybe there are lots of people who are/should be worried, despite the fact that you don't appear to be, because of the effects of that 'little' rise :

    1) The impacts of sea level rise - even in the lower ranges of the current predictions - looks to be severe. Approximately ten percent of the worlds population - 600 million people - live in low lying areas in danger of being flooded. A previously released study led by John Church, shows that even a modest sea level rise of 50 centimeters will result in a major increase in the number of coastal flooding events.

    "Our study centered on Australia showed that coastal flooding events that today we expect only once every hundred years will happen several times a year by 2100", says John Church.

    2) "According to the most recent sea-level-rise science, that's where we're heading," said lead researcher Jeremy L. Weiss, a senior research specialist in the UA's department of geosciences. "Impacts from sea-level rise could be erosion, temporary flooding and permanent inundation."

    The coastal municipalities the team identified had 40.5 million people living in them, according to the 2000 U.S. Census. Twenty of those cities have more than 300,000 inhabitants.

    3) One often-overlooked dimension is elevation. Ten percent of the world's population lives in coastal areas that are less than 10 meters (33 feet) above sea level, reports Balk and her colleagues. Although they only comprise about 2.2 percent of the world's land area, these low-elevation coastal zones (LECZs) are home to 600 million people. In addition, about 360 million people in LECZs live in urban areas which means that more people will be exposed to hazards such as sea-level rise and storm surges—phenomena that are expected to worsen as a result of global warming.

    The Effects of Rising Sea Levels

    Although inundation by increases in mean sea level over the 21st century and beyond will be a problem for unprotected low-lying areas, the most devastating impacts are likely to be associated with changes in extreme sea levels resulting from the passage of storms (e.g., Gornitz et al., 2002), especially as more intense tropical and extra-tropical storms are expected (Meehl et al., 2007). Simulations show that future changes are likely to be spatially variable, and a high level of detail can be modelled (see also Box 11.5 in Christensen et al. (2007).

    As for your disdain towards silted-up ports, I think you will find that the populations who inhabited ex-ports like Miletus, Ephesus, and Great Yarmouth (and other Kentish ports), among others, would want to argue with you about your definition of "cataclysmic" as it applies to peoples' lives and livelihoods.
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  12. Muoncounter

    Well from your point of view, my approach is not a problem since I support a swift march to 100% renewable energy use starting now. I think we could do it within 20 years if we had the will. The latest from Israel where they are trialling battery changing statinos for cars suggests the range problem with electric vehicles has been resolved, so we can now look at a more or less complete and all-embracing solution.

    My reasons for favouring 100% renewables are many and various but do include a precautionary approach to altering carbon levels. But to adopt a precautionary approach is not the same as saying I buy into the reality of AGW yet.

    My view is that sea level rises would happen sufficiently slowly for humanity to react effectively.

    No relation to that Maris!
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  13. Absolutely no denying the negative impact of raising the sea level, but I would like to post a few remarks.

    At the beginning of some “Sisyphean” working.

    @Tom Curtis
    Be very careful in interpreting the sea level during the Eemian. Another - the greater was the weight of the glaciers in the NH continents during the glaciation preceding the Eemian - another "post-glacial rebound”. In addition: “This may have been due to the fact that a large part of the ice sheet that today covers the western part of Antarctica did not yet exist.” “In the northern hemisphere, insolation was much higher than today during the summer months, and much lower during the winter ones, making seasonal contrasts much more acute.” (ibidem).
    Are also disputed the average global temperature Eemian - could be a more than 1-2 degrees C - more than - on average - in the twentieth century.

    Is the current rate of sea level rise - “what’s the big deal?”

    Looking at the Holocene - we can say: “During this ~5000 year period of high sea level, growth hiatuses in oyster beds and tubeworms and lower elevations of coral microatolls are interpreted to represent short-lived oscillations in sea-level of up to 1 m during two intervals, beginning c. 4800 and 3000 cal yr BP. The rates of sea level rise and fall (1–2 mm yr-1) during these centennial-scale oscillations are comparable with current rates of sea-level rise.”

    ... and the future (based on an understanding of the past)? - a problem to a separate discussion.
    I recommend especially the last sentence: ... "that there is much about interpreting the geologic record of sea-level variation that we still do not understand. (...)."
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    Moderator Response: [DB] And I especially like this sentence from earlier in your last linked source: "it could have risen quite quickly, as much as 2 meters per century, says geochemist and lead author Jeffrey Dorale". You assume SLR will be linear while your last linked source shows that it most likely was not. Hansen 2011 speaks to nonlinear destabilization of the ice sheets, with multiple meters of SLR occurring globally as a result. It may not be what you want to read, but the true skeptical mind considers more than just that which supports their position, to avoid confirmation bias.
  14. The headpost by Tamino asks about Houston and Dean "Why do they repeatedly drone on about “deceleration” when the average of the acceleration rates they measure, even for their extremely limited and restricted sample, isn’t statistically significant?"

    The answer is given in their paper. Looking at acceleration allows one to ignore glacial isostatic adjustments, which are one of the biggest unknowns when looking at sea level. Houston and Dean looked at tide gauge levels that did not have GIA applied. This can be done since it is a reasonable assumption that the isostatic rebound adjustments do not change over the less than 100 year period they studied.
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  15. Charlie A, please note Neil White's comment at Tamino

    It's quite relevant to your comment

    (and an "ouch" for Houston & Dean).
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  16. Marco, are you referring to Neil White's comment about Yukutat? White's comments not very relevant, since Houston and Dean excluded Yukutat from the analysis, along with 5 other outliers.
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  17. JMurphy -

    Humanity has always lived in "low-elevation coastal zones" - indeed many experts theorise they were a cradle of humanity. A rise in sea level won't make them disappear. All that will happen is that people will move with the sea. We've seen this in reverse, where ports and other areas have silted up. We see it on our Eastern coast in the UK where people are having to move inland as the coast erodes. It's sad for the people immediately affected but it is hardly a disaster.

    Even with coastal erosion, where the effects are much quicker than the sort of sea level rise being talked about here, we are able to cope with minimal casualties.

    Sea level rise would have to be v. dramatic to make much difference to the world.
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  18. Villabolo - Are you failing to account for the fact that ice is more expansive than water? I have read that melted ice in the Arctic for instance has no effect on sea level because of that scientific fact.
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  19. Tom Curtis -

    You talk of a "1 metre sea rise by 2110". Even assuming you are correct, that's 110 years off.

    Have you taken into account the impact of irrigation schemes? Water that used to run off into the sea is now pumped into dry desert areas and vapourises several times over - adding to the total amount of water vapour in the atmosphere. This could be offsetting sea level rise and such schemes will multiply hugely over the next 110 years.

    I have faith that in 11 decades' time we will have (a) have found a way of producing all our energy without adding carbon to the atmosphere and (b) found technical solutions to many of the big environmental problems.
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  20. daniel maris @19

    "I have faith that in 11 decades' time we will have (a) have found a way of producing all our energy without adding carbon to the atmosphere and (b) found technical solutions to many of the big environmental problems."

    I hope so, but the first step is admitting there is a problem. Many have yet to make it even that far.
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  21. daniel maris#18: "melted ice in the Arctic for instance has no effect on sea level "

    Perhaps more careful reading is in order. The Arctic is sea ice; it is floating on water. By itself, that means it has minimal impact on sea level rise. However, wither Arctic ice, so goeth Greenland's land-based ice - and that's a heck of a lot of water.
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  22. daniel maris wrote : "Humanity has always lived in "low-elevation coastal zones" - indeed many experts theorise they were a cradle of humanity. A rise in sea level won't make them disappear. All that will happen is that people will move with the sea."

    Cradle of humanity ? From human evolution and movement out of Africa, to the development of civilization around rivers like the Euphrates, Tigris and Nile, I'm not too sure about that. Even if true, how far inland can people move (in their millions, don't forget) as sea levels rise, and how do you think the millions already in those areas will feel about all those extra millions trying to move next to them ?
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  23. This is OT, but a location near Johannesburg has dibs on "cradle of human kind". And the Witwatersrand (on which Jo'burg is located) is about 1500 to 1700 m above sea level.

    Tamino's stats are in all likelihood correct.....the conclusions drawn from the paper in contention are based on a seriously flawed analysis and thus baseless, as are almost all 'skeptic' arguments.

    It is estimated that currently about 160 million people live below 1 m above sea level (Copenhagen Diagnosis). Wealthier nations may very well be able to adapt to rising sea levels, but even then building sea level defenses is incredibly expensive and an ongoing task (yet more money for maintenance). But let us not forget about those who do not have the resources for such luxuries, let us not forget Bangaldesh.
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  24. Aah, JMurphy stole my thunder. I shall have to start calling him Prometheus. :)

    Well, to salvage a comment: When the world emerged from the depths of the last ice age & the meltwater pulses flooded what humanity was then using for their civilizations at the time, there were perhaps only a few million humans worldwide.

    We are now pushing 7 billion persons on the globe...and struggling to feed them all. Combine the expected losses of some of the worlds most productive agricultural lands due to SLR with increasing drought and desertification, mix in societal instability and degraded & overtaxed infrastructures with hundreds of millions of climate change refugees along with nuclear-capable rogue states and you have a recipe for disaster.

    Those that remain will have a bit more room (a bit tough to grow crops under the harsh Arctic winter dark though), once the fighting wanes.

    The Yooper
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  25. Not wanting to go too far off-topic, but Prometheus also lived quite high up (on Mount Olympus) and was later (painfully) confined to the Caucasus (also mostly far from the sea), so none of that conforms to the "cradle of humanity" theory also - even if it is fanciful. As for my liver...
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  26. Daniel, do think the migration of say 100 million people away from salted deltas which can no longer sustain agriculture is going happen with no problems? When in history did we have a peaceful migration of even a 1/10 of the that magnitude. You will lose the deltas to salt and erosion long before they go underwater.
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  27. A further point - how easily humans adapted in the past can be deceptive. 2000 years ago, global population was around 200 million. By time of colonisation of America, it was still less than 1 billion. Moving a few people is much easier than moving a very large no. of them dependent on complex created infrastructure.
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  28. Albatross -

    If you knew anything about Bangladesh you'd know those delta islands are constantly forming and re-forming. Of all the people on Earth the Bangladeshis are probably best able to cope with sea level rise. Not that I blame the government making use of the issue to garner some more development funds.
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  29. Scaddenp,

    No I reject that. The Japanese government has just announced it is going rebuild a number of vulnerable coastal towns destroyed by the Tsunami on hillside locations. So it can be done.
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  30. Daniel Maris @19, 2110 is about 99 years of by my calendar.

    Water used in irrigation is, as you say, evaporated, but from there it joins the water cycle and ends up in the sea. The total effect on SL of the additional water vapour in the atmosphere due to irrigation, therefore, will be much less than the additional water vapour in the atmosphere due to higher temperatures- whose effect on SL is inconsequential.

    A better case can be made that the amount of water dammed by humans has reduced sea level (by about 1 mm from memory), but more water has been released from ground water into the water cycle than has been dammed, so the net effect of human interference with the water cycle has been a very slight increase in the rate of rise of SL - although inconsequential compared to thermal expansion and glacial melting.
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  31. "Cradle" was perhaps the wrong word. "Lifeline" might ahve been better because many experts think humanity spread out across the globe along the narrow coastal strips, where there was always a plentiful supply of seafood to keep them alive.
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  32. #28: "Of all the people on Earth the Bangladeshis are probably best able to cope with sea level rise."

    Yes, they've had lots of practice.

    The catastrophic flood of 1987 occurred throughout July and August and affected 57,300 km2 of land, (about 40% of the total area of the country) and was estimated as a once in 30-70 year event. ...

    The flood of 1988, which was also of catastrophic consequence, occurred throughout August and September. The waters inundated about 82,000 km2 of land, (about 60% of the area) and its return period was estimated at 50–100 years. ...

    In 1998, over 75% of the total area of the country was flooded. It was similar to the catastrophic flood of 1988 in terms of the extent of the flooding. ...

    The 2004 flood was very similar to the 1988 and 1998 floods with two thirds of the country under water.

    So that's four 50-100 year events in a period of 17 years. No problem, right?
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  33. Daniel, if you knew more about sea level rise, you would realise Bangladesh hasnt got a hope when sealevel rise overwhelms sediment deposition rates. You cant adapt to growing in salt and you cant adapt to living underwater. Have a look at WG2 for actual studies of consequences rather than guessing. The most vunerable deltas are Mekong, Nile, and Ganges. Where do those people go? And yes, bully for the Japanese - nice being rich - I'll bet they are not moving the farming though and that is the point, not the settlements.
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  34. #29: "The Japanese government has just announced it is going rebuild"

    That's hardly a done deal:
    Government sources said on Sunday the initiative includes buying urban areas that would be hard to reconstruct as well as encouraging people from coastal regions to move to higher places, DPA reported. ...

    However, the residents are likely to show resistance to the resettlement plan. Having predicted people's disagreement, the government is also working on a plan to develop urban residential regions that can resist a tsunami and thus allow people to continue to live near the sea.
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  35. The land inundate by sea water during the Tsunami in northeastern Japan is not going to be much use for agriculture for quite some time.

    A 1 m increase in sea level is expected to submerge about 17% of Bangladesh, 2 m would submerge its capital. And that is not taking into account the impact of storm surges superimposed on of higher sea levels. Here is but one of many publications on the subject.

    Also, consider this

    Ignoring these warnings is pure folly.
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  36. Albatross,

    But the point about a one metre rise is that it isn't going to happen in one year. It will be gradual, maybe spread over 100 years or more, and the Bangladeshi people in the delta are used to having to abandon land when it gets indundated.

    This will be a very gradual process. Presumably the delta will move back along the Ganges as the sea level rises.

    No doubt humanity will have to adapt to changed circumstances but the change will not be so severe as to preclude adaptation.
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  37. Daniel @36,

    "No doubt humanity will have to adapt to changed circumstances but the change will not be so severe as to preclude adaptation."

    That is your unsubstantiated opinion, fine, but governments cannot tackle this based on blind faith and wishful thinking. I am with the experts on this one.

    Yes, it is a creeping problem, nobody in the know said any different-- but it is a problem that is highlighted when one has floods or storm surges, and as you know Bangladesh is frequently affected by storms. But you are missing the point, adaptation has costs associated with it, both economic and social. So prevention is better than cure.

    I'm not sure whether or not you agree with Tamino's assessment/analysis-- the actual topic of this thread.
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  38. Moving from one delta island to a newly emergent one is fine, but as sealevel rises, there is no new island - the shoreline moves back toward already heavily populated lands. Migration at moment is move to slums of Dacca. This is problematic now at 3mm/yr. Worse at 10mm/yr There is no getting away from fact sealevel rise = loss of arable land. Farmland doesnt just move somewhere else. When aggradation exceeds progradation, the nature of coast line changes. If you want to see what 10mm/yr looks like, try places where sealevel rise is already like that from tectonic causes. Try this for a sustained 7-8mm/yr landscape.
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  39. Further to scaddenp's comment:

    The Nile Delta is one of the most heavily populated and intensely cultivated areas on earth. It is home to over one-third of the national population and produces nearly half of all Egypt's crops.

    Potential impact of sea level rise: Nile Delta. Rising sea level would destroy weak parts of the sand belt, which is essential for the protection of lagoons and the low-lying reclaimed lands in the Nile delta of Egypt (Mediterranean Sea). The impacts would be very serious: One third of Egypt's fish catches are made in the lagoons. Sea level rise would change the water quality and affect most fresh water fish. Valuable agricultural land would be inundated.
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  40. Arkadiusz Semczyszak @13, regardless of the difficulties of interpreting the evidence of past ages, doing so is still the best guide to what we should expect in the future with a changing climate. Given that, the Eemian with a nearly identical continental arrangement and mean global surface temperatures that are between 1 and 2 degrees greater than the mid 20th century mean makes an ideal test case. While some scientists may argue for a warmer Eemian temperatures, others, notably Jame Hansen, have recently argued for a much cooler Eemian temperature. Until such controversies are resolved, it seems judicious to use the most common, and midrange values. Even using the higher values is hardly cause to be sanguine, given that BAU scenarios predict temperature increases of 4 degrees or more, ie, more than twice the mid-range estimates for the Eemian.

    Having said that, the rest of your argument is self contradictory. You attribute the higher Eemian sea levels both to greater continental depression due to heavier ice sheets of the preceding glaciation, and to the near absence of the WAIS. That near absence would by itself account for a 3+ meter sea level rise, making your alternative explanation redundant. Given that south GIS melts sufficient to raise sea levels by 1 to 2 meters are consistent with continued ice at Dye 3; and further, given that the interpretation of the "Eemian" ice at the base of Dye 3 being controversial, with a strong possiblity that it represents new ice growing at the end of the Eemian, the case that a "small" increase in temperature of just 1 to 2 degrees will, given time lead to substantial melting of both the WAIS and the GIS with consequent 4-6m sea level rises seems hard to controvert.
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  41. @Moderator

    Well, we quote - but would not sense of to change the references cited.

    “Various researchers going back nearly a century have attempted to isolate the cause of the ice-age cycle. They have uncovered several factors--periodic changes in Earth's orbit around the sun, a wobble in our planet's axis of rotation, for example--that seem to be in play. But so far no one has presented the definitive answer.

    Conclusion 1. We do not know the causes, not only glacial cycle - but the rapid increase sea level.

    Conclusion second. Changes in the surface of the glacial (MIS) 5a were much higher than today.

    “That suggests the glaciers were melting at a tremendous rate. Even half that rate would still be "a major finding," Dorale says. So it "has major implications for future concerns with sea-level change."

    Agreed. Changes may be rapidly acceleration - and it's perfectly natural causes. Only a what changes?

    Still mysterious, however, are other data, taken from Barbados and New Guinea, that also suggest rising sea level about 80,000 years ago but not nearly as much of a change.

    So speaking about the global rate of sea level rise - this is a misunderstanding. Even at the present they are regions where sea levels are not rising - and even decreases (consensus - the majority - rising).

    This does not affect the application (by looking at the geological past) that significant (and rapid) changes in sea level - from natural causes - it is "standard ". C. The current 2-3 thousand. years, "peace" - is something "unusual" - except "to the rule".
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  42. It is hard to refute the notion that if all the ice in Greenland were to melt, the oceans would rise 7 or 8 meters (or whatever the new level turns out to be), as the concept only involves geometric considerations. On the other hand, for all that ice to melt, it requires a specific incremental energy expenditure over time. Furthermore, all that extra ocean water will be that much more of an energy sink for cooling the Earth, given that water in liquid form will do this more than ice that is currently trapped. Where I am going with this, is that the problem is more complex and tends to favor this event not happening so fast.
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  43. @Tom Curtis

    A propos Hansen’s paper: - “It was written in a bit of a rush when the editor told me there was a last chance to submit a paper before the book went to press,” - says Hansen in blog (...)
    That should be sufficient for us here ...

    I recommend the analysis (especially graphs - Fig . 3.) here: Holocene and Eemian sea surface temperature trends as revealed by alkenone and Mg/Ca paleothermometry, Leduc, et al., 2010., to be aware of our ignorance - regarding the differences - Eemian - Holocene.
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  44. Does the Agulhas Current amplify global temperatures during super-interglacials? Turney & Jones, 2010.:

    “Arguably one of the best super-interglacials for investigating this conundrum is the Last Interglacial (LIG), spanning the period ca. 130–116 ka ago and characterised by solar insolation anomalies caused by the changing Earth's orbit (Harrison et al., 1995; Otto-Bliesner et al., 2006). There is some uncertainty, however, regarding the global temperature during this period, with estimates ranging from 0.1 to >2°C warmer than present (CLIMAP Project Members, 1984; White, 1993; Hansen, 2005; Rohling et al., 2008).”

    “Greatly reduced Arctic sea ice area, changes in ice sheet topography and freshwater influences on the Atlantic Meridional Ocean Circulation (AMOC) have all been proposed as possible feedbacks for driving higher temperatures, but no consensus has been reached (Otto-Bliesner et al., 2006; Masson-Delmotte et al., 2010). Accompanying these changes, recent estimates of sea level corrected for changes in gravity, solid Earth deformation and other effects have suggested the LIG was 6.6–9.4 m higher than today ...”

    Conclusion: If only it was warmer by 0.1 deg C (Eemian - Holocene) is as much as 9?% difference in sea levels can be explained by factors other than temperature - 1.5 deg C - as they want the paper - it's 9?% difference in sea levels can be explained differences in temperature?

    Such is the extent of our understanding. For the practice of comparing Eemian - Holocene; is a purely "academic. "
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  45. 42 RSVP

    You want to be really careful making comments like that around here. Your outcome "nothing will happen" requires feedbacks, models, non-linear systems etc. etc. All things that climate change skeptics believe undermine any prediction.
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  46. AS @44

    The conclusion of Turney and Jones 2010?

    The Last Interglacial is an excellent example of a super-interglacial, a period warmer than today, where sea levels were 6.6–9.4 m higher than today, providing a valuable insight into the future climate system. Unfortunately, previous estimates of global and regional temperatures have been highly uncertain. Here we have compiled 263 quantified ice, marine and terrestrial records spanning the Last Interglacial. Although only a first approximation of published datasets, our results suggest this period was approximately 1.5°C warmer than AD 1961–1990 (∼1.9°C relative to pre-industrial levels). A comparison between the reconstructed temperature and δ18O trends in the highest-resolved records preserves a stratigraphic lead in ‘local’ warming over the shift to interglacial conditions around the southern African coastline. These results imply an enhanced leakage of the Agulhas Current into the Atlantic Ocean, injecting warm, saline water into the meridional ocean circulation and amplifying global warming during this super-interglacial. The above observations suggest the LIG can provide important insights into the mechanisms of future climate and whether a 2°C stabilisation scenario can be considered ‘safe’.

    (My emphasis)

    As the authors conclude that the Eemian can provide the sort of insights I am taking from it, it seems hard to conclude the paper provides evidence that you cannot. Certainly taking the lowest extreme of temperature estimates with the upper limit of SL estimates to argue that temperature is not the explanation of the SL rise is unwarranted. Indeed, it is the sort of argument that has all the hallmarks of pseudoscience. Discussed in context the paper supports the conclusion that relatively low (1.5 degree) temperature increases could result in long term sea level rises as great as 9 meters.

    And as an aside, as the ocean is much deeper than 100 meters, a 9 meter sea level rise is not a 9% rise.

    Likewise for the paper discussed by AS in 43. It contains an interesting discussion of detecting seasonal temperature variations over the holocene, which should greatly refine future temperature estimates. But fig 3 deal only with Holocene temperatures. The authors do not call Eemian temperature records into question, but rather use them as a test of their theory of the main driver of regional SST in the Holocene. In other words, they consider them generally accurate, and reliable enough for hypothesis testing.

    AS's skepticism about Eemian temperature records is something he brings to these papers, not something he finds in them.
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  47. Albatross -

    Bangladesh has ALWAYS been afflicted by tremendous storms that destroy islands and redistribute silt etc.

    Logicman -

    You aren't saying the Nile Delta has always been where it is now are you? Deltas move and grow over time. Let's suppose there was a one metre rise in sea level - is it really beyond the ability of Egypt to use its waste to build up those islands - as the Dutch have done?

    Les -

    I wouldn't deny that at least one prediction might be broadly correct. The question is how to identify the correct prediction. Climate seems a pretty complex system, perhaps too complex for computer modelling - especially when you go back into the past, times when animal and vegetable life might have affected outcomes.
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  48. Daniel,

    With respect, if you are going to try and obfuscate here, you are going to have to do better and back up your assertions with science, otherwise you will only sound like a D-K and your personal opinions will not be taken seriously nor will they be compelling.

    "Bangladesh has ALWAYS been afflicted by tremendous storms that destroy islands and redistribute silt etc."

    A blatant strawman. I have never denied that. The issue, which you seem intent on missing, is the impact of a storm surge of say 5 ft being superimposed on a sea level increase from AGW. The underlying increase in sea-levels will only go to aggravate the impacts from the storms, just as the underlying warming trend has exacerbated recent heat waves in Europe and elsewhere.

    With AGW, it is the shift in the tail of the distribution that are going to make the greatest impacts, and that is what people intend designing and planning for in advance.

    I asked you earlier about your thoughts on Tamino's analysis? Care to please speak to that?
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  49. dm#47: "is it really beyond the ability of Egypt to use its waste to build up those islands"

    For a country without a fully functional government and an economy in tatters, it may well be. Consider that things may get worse economically; such large reclamations may well be beyond all of our means. Look, for example, at how the lack of sustainable work done at the federal level to fix problems in New Orleans and points further south along the Mississippi.

    "Climate seems a pretty complex system, perhaps too complex for computer modelling ... "

    Ah, the old dodge: it's too complex to model. Suggest you look at the 'modeling is reliable' thread, the 'chaotic systems' thread, etc. Use the Search function.

    " ... especially when you go back into the past, times when animal and vegetable life might have affected outcomes. "

    What is this supposed to mean? And what relevance does it have to the measurable changes in sea level rise that are the topic of this post? Is your basic interpretation of this and related problem merely 'let's wait and see?'
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  50. #47 - Daniel

    "You aren't saying the Nile Delta has always been where it is now are you?"
    Of course I'm not! 'Always' is the age of the universe!

    "Deltas move and grow over time."
    Ah! A variant of the 'natural cycles' gambit.

    "is it really beyond the ability of Egypt to use its waste to build up those islands"
    They have been doing that for millennia. Since the Aswan dam was built they have had to do it more.

    The Aswan dam blocks about 12 million tonnes of silt that used to replace delta losses from sea erosion. The silt used to fertilize the region: agriculture now depends on artificial fertilizers.

    Sea level rise will compound Egypt's existing agricultural production problems.

    Most of the world's population lives in coastal regions.
    Sea level rise means that most of the world's population will see dramatic evidence of a predicted outcome of global warming before the year 2100.
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